21/09/2017
iBGP – eBGP
| eBGP | iBGP | |
|---|---|---|
| External BGP | Internal BGP | |
| Neighbor | Between differnet AS | Within the same AS |
| Route updates | Routes are send to eBGP peers by default | Routes are not send to BGP peers by default |
| AS path addition | yes | no |
| Administrative distance | 20 | 200 |
| Topology | Does not require a full mesh | Full mesh or Route reflectors or Confedoration |
| Loop Prevention | as-path | BGP split horizon |
eBGP
- 3 steps to get best routes;
- Form a neighbor relationship.
- router bgp 1000
- neighbor 10.10.10.10 remote-as 2000
- Exchange topology information.
- Run a best-path algorithm
- Form a neighbor relationship.
- Assumed to be directly connected (apart from multihop)
eBGP neighborship requirements
- Peer must be reachable via an IGP route.
- BGP router IDs cannot be the same.
- Authentication must match.
- Router must complete a TCP connection (tcp 3 way handshake) with the BGP peer.
- Source adress must match the other side’s BGP neighbor command.
R1#(config)router bgp 10 R1#(config-router)neighbor 20.20.20.20 remote-as 20 R2#(config)router bgp 20 R2#(config-router)neighbor 10.10.10.10 remote-as 10
iBGP neighborship requirements
- Must be in the same AS as the iBGP peer.
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